The definition of "cover letter," according to the Oxford English Dictionary, is "a letter sent with, and explaining the contents of, another document..."

The resume is the document and the cover letter explains it.

A cover letter is an opportunity to introduce yourself, summarize and explain why your skill set and qualifications make you the ideal candidate, and tell the employer what you can do for them. A well-crafted cover letter is a no-brainer if you want to stand out among other candidates.

Put yourself in the employer's shoes. If you received a piece of paper in the mail with a list of skills, education, and work experience from someone you'd never met, would you be inspired to write this person back or call them up to come work with you? Probably not. If you received that same list of skills, education, and work experience in the mail along with a personalized letter addressed to you, crafted to tell you specifically what that person could do for you, would you be inclined to write back or call them up to come work with you? Probably.

There's a certain vibe that comes with pairing a cover letter with your resume. A well-written cover letter exudes confidence and allows you to be personable, tell a story, and express a bit of "you." The hiring team will get a glimpse of what you're all about before making a commitment to interview you. You can help make their decision an easy one.

Which, from the two candidates below, would you pick?

This is where I studied during these dates. This is where I worked during these dates. These are my super awesome skills and qualifications. PICK ME!

This is where I studied during these dates. This is where I worked during these dates. These are my super awesome skills and qualifications.

Let me tell you a bit about myself and explain why my education and work experience make me the ideal candidate for the position. This is what I can do for you and your company. I look forward to meeting you and discussing my qualifications in more detail.

HR departments and hiring managers will select and engage with candidates who show that they care. The candidates who are truly interested in and passionate about the job are the ones who take the time to write a unique cover letter, even if it's not a requirement of the job application. These candidates know to whom they should address a cover letter, they research the values, mission statement, and current projects of the employer they wish to work for. You can be one of these candidates. It's always worth the extra time and effort.

Resume expert Natalie Severt points out that directly addressing someone in a cover letter with “Dear Jane Smith” instead of “To whom it may concern” is scientifically proven to be more effective.

It might seem daunting to think that you must write a separate cover letter and research the name of the hiring manager for each resume you send out. Job seekers often send dozens upon dozens of resumes in hopes of landing employment, but it's far more effective to send 10 resumes with an exceptionally written, custom cover letter than to send out 100 resumes with a generic cover letter or no cover letter at all.

In 2016, 45 per cent of recruiters rejected resumes without a cover letter, according to stats released by Careerbuilder. And career and editorial coach/writer Sara McCord says that non-specific, generic cover letters beginning with "To whom it may concern" are sure to land in her "no" pile.

The likelihood of you landing an interview by sending in a resume on its own is slim, especially considering the slew of candidates applying for jobs. The exception is when you're applying online and there's no place to upload one. But honestly, if I really wanted/needed the job, I would go the extra mile and contact the company to find out who the hiring manager was for that position, write a cover letter to him/her, and email it (along with my resume) straight to that person's inbox.

According to job and recruiting site Glassdoor, corporate job openings attract 250 applicants. Only 4-6 people land an interview.

When the majority of your competitors won't bother to write a cover letter, you are sure to give yourself a head start by including one.

Tip: If you aren't going to spend the time to compose a strong, custom cover letter, you might be better off without it. A poorly written or slapped-together letter doesn't win anybody over. Think of the cover letter as a sample of your writing ability; you don't want to give recruiters a reason to reject your application.